Torque transmission systems which interconnect a drive shaft to a parallel, driven shaft conventionally employ chain or belt torque transfer systems which operatively connect the parallel shafts, each of which has a sprocket or pulley of different pitch diameter to produce a fixed-speed drive ratio therebetween. To provide even a two-speed drive ratio between such shafts has historically required a rather complex arrangement of gears and torque transfer devices, the latter generally comprising clutches and/or brakes. To change the speed of the drive ratios with the prior known arrangements has required shift clutches and intermeshing gears with bearings and rotating components, each of which contribute to losses in overall efficiency.
Another somewhat less expensive but no less technically complex arrangement has employed multiple sprockets on each shaft. In that arrangement, the sprockets on one shaft are each aligned with sprockets on the other shaft, and a chain drive selectively interconnects the aligned pairs of sprockets. A derailleur selectively transfers engagement of the chain drive between the aligned pairs of sprockets so that the drive ratios can be selected between those provided by the pairs of aligned sprockets.
Because of the costs to manufacture and maintain, the prior art arrangements as well as the need to remove the load during the shift, many parallel shaft installations are simply provided with a fixed-speed drive ratio. Such a fixed-speed drive ratio provides a weighted average or compromise between the highest and lowest drive ratios desired for a particular installation. In short, the prior known structural arrangements which provide selective drive ratios are overly sophisticated and overly expensive to be employed in many torque transmission systems for which they are desired, and for which they would be beneficial, were it not for the overall costs and complexity of the structures heretofore available for providing selective drive ratios.